Conventional containers for beverages are constructed so that the upper end opening of the container is covered and sealed with a lid. In this type of beverage container, the container is filled with beverage after the container interior has been sterilized to provide an aseptic state.
Known lids for the aforementioned types of containers typically take one of several forms. A lid of the so-called peelable seal type (hereinafter referred to as membrane type), which is made of a sheet including a stretched PET (polyethylene terephthalate) film, is laminated on the surface of an aluminum foil layer, and an easy peel layer is provided on the side thereof which comes into contact with the container. The lid is mounted to cover the open upper end of the container and is fuse-bonded in place by heating.
Another form of lid involves a sheet that covers the open upper end of a container and is provided with an opening that serves as a drinking or discharge hole. The lid has a pull tab covering the opening, with the pull tab being formed from a small piece of PET/aluminum foil having an easy peel layer.
A different lid construction is one in which the lid is shaped by draw-forming aluminum foil.
A further type of lid construction involves preparing the lid by so-called insert injection molding in which an aluminum foil coated with PE (polyethylene) is previously inserted into a mold and in which the lid having a desired opening means in the aluminum foil is molded by injection molding.
The above-described forms of conventional lids suffer from a variety of drawbacks and disadvantages. For example, in the membrane type lid described above, the seal strength between the lid and the container must be high enough to withstand handling during transportation of the products. On the other hand, the opening strength required for removing the lid from the container should not be so high that opening of the lid is made excessively difficult. It can be appreciated that it is oftentimes difficult to balance these two requirements.
Further, since the opening in the container that results after the removal of the lid from the container is rather large, an inconvenience arises in that the beverage is apt to spill when, for example, the beverage in the container is being consumed while walking.
In the case of the above-described lid having a pull tab, the problems associated with the membrane type lid are not as prevalent. However, since the pull tab is formed of a membrane-type sheet, the lid does not present a high quality feeling but rather gives a somewhat "cheap-looking" appearance or impression to the lid.
The above-described lid in which an aluminum foil is draw-formed suffers from the drawback that it is relatively expensive.
The last type of lid described above possesses gas-barrier properties, but is nevertheless problematic because coating the aluminum foil with PE is complicated and the lid is susceptible of being easily peeled off.
Most of the above conventional lids are removed and separated from the beverage container after the container has been opened so that a disposal problem for the lid also arises. Even in the case of a lid which is not removed from the container at the time of opening, the current technology is such that the opened container cannot be sealed again with the lid.